Browsing by Author "Tsao, SL"

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Inter-working and integration of messaging services in a heterogeneous wireless environment
(2005)
Tsao, SL
;
Chou, JC
;
Hsu, YC
;
資訊工程學系
;
Department of Computer Science
Messaging service such as email, short message, instant messaging and etc. has become one of the most important applications in both Internet and personal communication systems. Unfortunately, most of the messaging systems are not interoperable, and users using different systems might not be able to communicate with each other. Besides the message inter-working issue, to facilitate users accessing their messages through the preferred devices, networks and messaging systems at anytime and anywhere is also an important feature for a future messaging system. In this paper, we present a generic inter-working and integration architecture of messaging systems in a heterogeneous wireless environment. By employing the architecture, different messaging systems can be easily integrated, and provide users a pervasive messaging service. A prototype system based on this concept is thus implemented to demonstrate the correctness of the proposed architecture and design.
Reducing idle mode power consumption of cellular/VoWLAN dual mode mobiles
(2005)
Tsao, SL
;
Cheng, EC
;
資訊工程學系
;
Department of Computer Science
The integration of cellular and voice over WLAN (VoWLAN) systems recently has attracted considerable interest from both academia and industry. A cellular/VoWLAN dual mode system helps mobile users to access a low cost voice over IP (VoIP) service in a WLAN area and switch to a wide-coverage cellular system without WLANs. However, the system suffers the power consumption problem and the service continuity issue between cellular and WLAN systems. This study presents a network architecture for an enterprise or a dual mode service provider to permit service continuity between cellular and VoWLAN systems. This architecture is used as a basis for further elaborating a novel power saving mechanism, called PIANO (paging via another radio). By applying the proposed mechanisms to a dual mode mobile, the mobile can completely switch off its WLAN interface, only leaving the cellular interface awake to listen to paging signals. When a dual mode mobile receives a paging message from its cellular interface, it wakes up its WLAN interface and responds to the call via WLAN networks. Therefore, a dual mode mobile can reduce the idle mode power consumption, and can also obtain VoWLAN services. The simulation results illustrate that the proposed methods significantly extend the standby hours of a dual mode mobile.
Research challenges and perspectives of voice over wireless LAN
(2005)
Tsao, SL
;
資訊工程學系
;
Department of Computer Science
Wireless local area network (WLAN) has been widely deployed in recent several years. Voice over IP over WLAN, or called voice over WLAN (VaWLAN or Wi-Fi phone), is regarded as one the killer applications for public and private WLANs. However, VoWLAN suffers from a number of technical challenges that make the commercial and large VoWLAN services difficult to provide. lit this paper, we brief the current technology status and summarize research challenges of VoWLAN services.